Diode coupling system



March 3, 1936.

A. CROSSLEY ET AL 2,032,914 DIODE COUPLING SYSTEM Filed Aug. 3, 1935 HP jF f7 I Z5; w 29 ou-rPUT EAT'O EINPUT INVENTORS, Z ALF/2E0 62 551.15;

' BY HEEBEETE/VE/NEMA,

ATTORNEY.

Patented Mar. 3, 1936 UNITED STATES PATENT OFFICE 111., assignors to Johnson Laboratories,

Inc., Chicago, 111., a corporation of Illinois ApplicationAugust 3, 1935, Serial No. 34,535

6 Claims.

The invention relates to improvements in vacuum-tube amplifying systems, and more speciflcally to improvements in the means for coupling the output of a vacuum-tube amplifier to the apparatus which follows the amplifier.

An object of the invention is to provide an improved means for coupling the output of a vacuum-tube amplifier to one or more diode rectifiers.

An additional object of the invention is to provide a coupling means for use between a vacuumtube amplifier and one or more diode rectifiers, so arranged that its performance is substantially uniform over a wide range of frequencies.

A further object of the invention is to provide a simple, compact and inexpensive arrangement for efllciently coupling one or more diode rectifiers to the output of a vacuum-tube amplifier of the type intended to cover a wide range of high frequencies.

When vacuum-tube amplifiers are used to ampliiy modulated high-frequency signals, it is the usual practice to employ one or more diode recti fiers coupled to the output of the amplifier. One

rectifier may act as a detector or demodulator, to separate the modulation component from the carrier component of the amplified signal. A second rectifier may be used to rectify the carrier to supply a direct-current voltage forautomatlcally regulating the amplification of one or more of the amplifying vacuum tubes or for any other purpose.

If the amplifier is of the type which is tunable over a wide range of high frequencies, it is dimcult to couple the diode rectifiers, which are of relatively low impedance, efficiently to the out put oi the amplifier, which is usually of relatively high impedance. If the rectifiers are coupled to a tuned circuit, they have a serious tendency to load and therefore appreciably broaden the selectivity of the tuned circuit. If, on the other hand, the rectifiers are coupled in the ordinary manner to the plate circuit of an amplifying vacuum tube, the performance usually lacks uniformity over a wide range of frequencies, such for example as the broadcast band of frequencies (550 001500 kilocycles per second). i

The arrangement of the present invention,

5 however, permits the rectiflers to be coupled to the plate circuit of an amplifying vacuum tube in an emcient manner which provides substantially uniform performance over a-wide range of fre quencies. The tuned circuits of the amplifier 55 are substantially unafiected, and the means employed foraccomplishing the coupling is simple,

compact and inexpensive.

The present invention will be better understood by reference to the drawing, in which Figure 1 is a schematic diagram of an em- 5' bodiment of the present invention; and

Figure 2 shows the performance of a coupling system arranged in accordance with the schematic diagram of Figure 1.

Referring to Fig. 1, the plate circuit oi ampli- 1o i'ying vacuum tube 0 includes inductor 2, resistor t, B battery 6, and self-biasing resistor 5, bypassed by capacitor t. The screen-grid l of vacuum tube 8 is connected to a tap on battery 6, and is by-passed to the cathode t by capacitor 9. 15 Control-grid it is connected to input terminal ii, and input terminal i 2 is connected to the junction of battery t and resistor 5.

Signal diode anode it of vacuum tube it is coupled to the plate Q5 of vacuum tube i by means 20 of blocking capacitor i6, and is connected to the cathode i l of vacuum tube it by load resistor i8. Likewise, control diode anode id of vacuum tube M is coupled to the plate 55 of vacuum tube 8 by means of blocking capacitor Eli, and is grounded 25 through load resistor 2i. Cathode it of vacuum tube i 4 is grounded through resistor 22, by-passed by capacitor 28.

The modulation voltages which apmar across load resistor 58 are tapped ofi through the-re- 30 sistor-capacitor filter 26, 25 and blocking capacitor 26, and made available at terminal ii. The

direct-current control voltages which appear across load resistor iii are filtered by series re-= sistor it and shunt capacitor is, and are made 35 available at -vial 3d.

Inductor 2 is so designed that, in conjunction with the associated networks, it is resonant at a frequency approximately midway between the era-- treme frequencies at which the system may be 40 used, and resistor t is so chosen as to materially decrease the sharpness of resonance of the network. The usual values of blocking capacitors it and Maud of load resistors id and 2i are such that they place a variable load on the plate cir- 4.5 cult and thus produce a substantially fiat gain characteristic over the frequency range, as illustrated in Fig. 2.

.In operation, a portion oi the high-frequency current which flows in the-plate circuit of vacuum tube I is tapped oil by capacitor it and rectified by diode anode i3 operating in conjunction with cathode i! of vacuum tube i l. The steady direct-current potential which appears across load resistor i8 is blocked by capacitor 26, but the output terminal 21.

appear between terminal 21 and ground. Filter 24, 2! prevents the high-frequency voltage which is present across resistor is from reaching the Another portion of the high-frequency current in the plate circuit of vacuum of! by means of capacitor 20 and rectified by diode anode is operating in conjunction with cathode ll of vacuum tube ll. corresponding with the modulation which are developed across load resistor 2|, are prevented from reaching the control output terminal II .by filter 2|, 22, but the steady direct-current potential which is present across load resistor 2iis also present between terminal 22 and ground; If a delay voltage is developed across resistor '22, no voltage will appear across load resistor 2i until the amplitude of the impressed high-frequency .voltage across resistor 2i exceeds the delay voltage.

In a successful embodiment of the invention, the following constants were employed:

. Resistor 2 -5000 ohms Battery 4 "250 volts (tapped at 100 volts), Resistor 5 -.400 ohms Capacitor l 0.1 microfarad- Capacitor 9- 0.1 microfarad Capacitor I8 .200 micromicrofarads Resistor IL-.. -01.0 megohm Capacitor "n uron micromicrofarads Resistor 2i .....1.0 megohm Y Resistor 22.. .l500 ohms Capacitor 22 .0.1 microfarad Resistor 24 .0.2 megohm Capacitor 25 ""500 micromicrof Capacitor 28----..092 microfarad Resistor 2i .1.0 megohm Capacitor; 28 0.01 microfarad When the system is intended to operate uniformly over the'usual broadcast range. the reactance of inductor 2 may be of the order of 2500 ohms at 1000 kilocycles, which .is about half the value of resistor 2.

It will be understood that these constants may be varied and that various modifications, as for example the use of a single rectifier for both detection and control purposes, may be employed without departing from the scope of the invention.

Referring to Fig. the ratio of the output voltage to the input voltage of the coupling arrangement is shown plotted against frequency. The input voltage is taken between grid II and ground, and the output voltage across resistor, or between diode anode i2 and ground. The curve shows a slight peak at the resonant frequency of the inductor 2 and associated network,

the flatness of the peak being due to resistor 2 in series with inductor 3 and the variable impedance of the entire network. The gain characteristic may be altered if desired by varying the values of the inductor 2 and resistor 2.

In a preferred embodiment, inductor 2 is of multiple-section, low-loss construction, but any suitable type of inductor may be employed without departing from the scope of the invention.

It will be understood that battery 4 maybe replaced by any suitable direct-current source. Furthermore, vacuum tubes l and I4 may be replaced by a single vacuum tube containing both amplifying and diode rectifyin P rtions,

tube i is tapped The pulsating voltages,

If the amplifier with which the arrangements of the present invention are to be used operates over a narrow band of frequencies, for example in the intermediate-frequency amplifier of a superheterodyne radio receiver, the inductor 2 with its associated capacitive-resistive network may be so designed-that it resonates at the nominal operating frequency of the amplifier, and the sharpness of resonance may be increased to a desired degree by lowering the value of resistor l.

' The arrangements of the present invention are especially adapted foruse in a compact radio receiver of the tuned radio-frequency type. in which it is desired to obtain automatic amplification control with a minimum effect upon the overall efficiency and uniformity of performance over the broadcast band of frequencies. If a very simple and inexpensive arrangement is required, a single diode may be used to supply both the audio-frequency output and direct-current voltages for control purposes. In this case, the automatic amplification control will operate without voltage delay. On the other hand, a very satisfactory delayed automatic amplification control is obtained by utilizing the arrangements disclosed herein.

It will be understood that the invention is not limited to the use of the control voltage for automatic amplification control. The control voltage may be used in addition or independently to control the fidelity or the selectivity of the receiver or in any other desired manner. also be understood that the present invention is not limited in its application to radio receivers, but that it may be employed with equal success in other types of vacuum-tube amplifiers, well as in receivers of types not herein specifically mentioned.

Having thus described our invention, what we claim is: 1

1. A high-frequency system including a thermionic amplifier having an anode circuit, at least one diode rectifier, an inductor and a resistor in series in said anode circuit, and a capacitor connected between a high-potential point in said anode circuit and said rectifier, said inductor and said resistor being so proportioned with respect to the load placed upon said amplifier by said rectifier that the amplification of said system is substantially constant throughout a desired range of frequencies.

2. A high-frequency system for operation over a range of frequencies including a thermionic amplifier having an anode circuit, at least one diode rectifier, an inductor and a resistor in series in said anode circuit, and capacitive coupling from said anode circuit to said rectifier, said inductor having a natural frequency approximately at the center of said range, said resistor being so proportioned with respect to the load placed upon said amplifier by said rectifier that the amplification of said system is substantially constant throughout said range.

8. A high-frequency system for operation over a range of frequencies including a thermionic amplifier having an anode circuit, at least one diode Itwillrectifier, an inductor and a resistor in series in oeenis rectifier, an inductor and a resistor in series in said anode circuit and capacitive coupling from said anode circuit to said rectifier, said inductor having a natural frequency within ssid reuse, said resistor being so proportioned with respect to tire iced pieced upon said amplifier by said rectifier that the resonant peak due to the nstursi fre quency of said inductor is substsntisiiy sup pressed.

5. A high-frequency system for operation over a. range of frequencies including o, thermionio em= piifier having an anode circuit, atieest one mcti= fier, an inductor and a resistor in series in stud anode circuit, and a. capacitor connected between e high-potential point in said anode circuit and said rectifier, the resctsnce of said inductor at the middle frequency of said range being substantially one-half the resistance of said resistor. I

6. A high-frequency system for operation over e, range of frequencies including a thermionic ompiifier having an anode circuit, at least one rectifier, and 8t cepscitor connected between a highpotentisi point in said anode circuit and said rectifier, and means inciuding an inductor and e resistor in series in said anode circuit iormsin tanning the snipiiiicetion of said system substem tsiiyconstsnt throughout said reuse.

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